In a ruling that could force the NYPD to reform its rules for dealing with emotionally disturbed suspects, a federal judge on Thursday said the cops who responded to Mohamed Bah’s Harlem apartment in 2012 had no “reason to believe” he “posed a threat to anyone” before breaking down his door and fatally shooting him.

In a 24-page ruling, Manhattan federal Judge Kevin Castel said he is allowing most of the claims to move forward in an explosive negligence lawsuit against both the city and cops who responded to a 911 call from Bah’s mother seeking medical help for her son.

“This is a very significant decision that says officers have no right to break down a door and Taser and shoot someone because they won’t open the door,” Bah family lawyer Randolph M. McLaughlin, of the law firm Newman Ferrara, told The Post.

Castel noted that the amended lawsuit — first reported by The Post in December — “plausibly alleges” that the officers’ “entry was unlawful.” He did toss out negligent claims in the suit against the city and the officers, but allowed other claims — including ones accusing the cops of unlawful entry and not being properly supervised — to move forward.

Bah’s mother, Hawa Bah.Photo: Warzer Jaff

McLauglin said the order backs the Bah family’s belief that “unlawful entry” was involved in the 28-year-old emotionally disturbed man’s death.

He called on Mayor Bill de Blasio and the NYPD to revise its regulations for approaching the emotionally disturbed so that a tragedy “like this never happens again.”

The suit claims cops fired 10 bullets at Bah because a confused officer screamed out that he was being stabbed — when the officer had accidentally been Tasered by a colleague.

Police claim the officers who responded to Bah’s Harlem apartment opened fire — fatally hitting him with eight bullets — because he was lunging at them with a knife.

When they entered the dimly lit apartment, cops tried to subdue the African immigrant with Tasers and guns firing rubber pellets.

The lawsuit also claims the Guinean native was still alive, although barely, after being shot — but then was callously “dragged” by authorities through the building’s hallways, leaving a trail of “smeared” blood.

In November, a grand jury empaneled by Manhattan DA Cyrus Vance found the cops were justified in using deadly force and shouldn’t face criminal charges.

The Bah family’s lawsuit relies on eyewitness accounts, police reports and other official documents.

It quotes Bah’s mother as saying her son was still alive, if barely, when emergency responders tried reviving him outside the building.

He died soon afterward at a local hospital.

Among the defendants named in the suit are the city and the three cops who are believed to have fired the fatal shots: Mateo, Andrew Kress and Michael Green.

A Law Department spokesperson issued a statement saying, “the judge has simply allowed certain claims in the lawsuit — which the city disputes — to go forward.”

“He has made no findings,” the spokesperson added. “The city will vigorously defend this lawsuit.”